I am using Eclipse now for php dev things. On my laptop I was very unsatisfied with the performance of Eclipse, even though I have enough RAM it was too slow.
This is only because when you install Eclipse with apt-get it uses the slower java-gcj vm. To change this first install the Java VM from Sun if not already done.
Next go to /etc/eclipse/java_home and uncomment the first line which looks like:
#/usr/lib/jvm/java-gcj
Afterwards I added a new line which points to SUNs JVM:
/usr/lib/jvm/java-6-sun-1.6.0.00
Edit: To install Java from Sun you have to
sudo aptitude install sun-java6-jdk
then with
java -version you will get the running version
and define it as a default
sudo update-java-alternatives -s java-1.6.0-sun
How do you know what type of JRE you are running. Maybe posting your java -version output before and after will help.